This application claims priority from French application 00 07778, filed Jun. 19, 2000.
The invention relates to the field of gliding sports and, more particularly, of Alpine skiing. It concerns more precisely Alpine skis equipped with mounting platforms for the elements of the binding.
It is generally known to equip the upper face of an Alpine ski with a mounting platform intended to hold the elements of the binding, namely the toe piece and the heel piece.
This type of platform fulfills several functions, in particular that of raising the level of the toe piece and of the binding in order, for example, to prevent the sides of the boot from coming into contact with the snow when the board is inclined.
In the large majority of cases, the platforms are produced by manufacturers other than those who develop and market the skis. Further, these platforms are most often sold so that they can be fitted on any commercially available ski, irrespective of its brand and its features.
A constant concern with this type of platform involves the interaction of the stiffness of the platform with the intrinsic stiffness of the board. To be precise, in particular depending on how it is anchored on the upper face of the ski, the platform inevitably increases the stiffness of the assembly and therefore interferes with the intrinsic stiffness of the board, whose structure and dimensions are designed so that it exhibits specific mechanical properties.
This is why, in general, it is desirable to limit the influence of the stiffness of the platform with respect to that of the board. Hence, as is known, the platform is fitted on the ski so that at least one of its ends has a capacity for longitudinal relative movement in relation to the board.
Solutions of this type have been described, in particular, U.S. Pat. No. 4,896,895. The platforms described in this document have an end which comprises an elongate opening, inside which a member secured to the upper face of the ski can slide. Since the other end of the platform is firmly anchored in the board, the various bending movements of the board cause one end of the platform to slide in relation to the upper face of the board. This limits the influence of the stiffness of the platform with respect to that of the board. Such a decoupling phenomenon is generally desired.
Other embodiments, such as the one illustrated U.S. Pat. No. 2,560,693, use a platform that is fixed by its central part in the ski, and each end of which is connected to the upper face of the ski so as to permit relative displacement by longitudinal sliding.
German Patent No. DE 4 317 675, corresponding to U.S. Pat. No. 5,474,321, describes another type of platform comprising a central support zone through which elements for binding to the ski pass. The front and rear ends of this platform are cantilevered above the upper surface of the board.
All these solutions aim to reduce the rigidifying side effect which the ski receives from the platform, in order to let the ski keep the mechanical features which were defined for it by its designer so that it complies with a specific product range.
One problem which the invention proposes to solve is that of integrating the stiffness features of the platform with the stiffness of the ski, starting with the design of the latter. Since the platform is an extra part attached to the ski, the means for anchoring on the ski, like the connecting surfaces between the ski and the platform, need to satisfy a number of constraints.
To be precise, it will be understood that when the two ends of the board are firmly anchored by screwing, for example, on the upper face of the board, excessive mechanical stresses are created in the screws or the means for anchoring the platform on the board, because the platform is relatively rigid.
Very large shear forces are exerted on the screws when the board deforms while, conversely, the platform stays straight.
One problem which the invention proposes to solve is that of providing the board/platform assembly with controlled rigidity, while allowing the platform to be anchored in a mechanically reliable and efficient way.
The invention relates to an Alpine ski having a boot middle mark or point indicating the position of the middle of the boot, and equipped with a mounting platform comprising front, central and rear zones.
This assembly is characterized in that:
the platform rests on the ski via three feet situated respectively in the front, central and rear zones of the platform, the height measured between the lower face of the foot and the upper face of the platform being a minimum for the foot situated in the central zone;
the platform is anchored without sliding on the ski at least in the front and central zones, the anchoring point situated in the central zone being positioned in front of the boot middle point situated on the ski, the anchoring points being separated longitudinally by a distance of between 150 and 300 millimeters;
the ski comprises a block of elastic material inserted between the front end of the platform and a support zone situated in front of the platform, said block being compressible during the relative movements of the platform in relation to the upper face of the ski, due to bending of the latter.
In other words, the platform bears on the board at three points forming support wedges, the thicknesses of which are determined so as to avoid compromising the natural curvature of the board, the thickness of which is a maximum in proximity to the central zone of the platform.
The stresses exerted on the anchoring foot are also reduced to some extent by the presence of a compressible element situated in front of and/or behind the ends of the platform.
Further, it has been observed that the stresses exerted on the front and central anchoring points are acceptable, without weakening the assembly, if the two points are separated by a distance of less than 300 millimeters and, on the other hand, if the platform acts in opposition to the deformation of the ski via the elastic block inserted between the end of the platform and the support zone situated on the ski, facing the end of the platform.
Further, it has been observed that the stresses exerted on the anchoring screws are less when the platform is screwed onto the board in front of the boot middle point.
In practice, the feet of the platform may consist of extra independent elements that form a support wedge and are fitted between the lower face of the platform and the upper face of the board, or which alternatively are an integral part of the platform and form protuberances under the lower face of the latter.
In practice, good results have been obtained concerning the ability of the anchoring screws to withstand forces when the intermediate anchoring point is situated in the central zone of the platform, but without necessarily being situated in the geometrical middle of the latter.
In a preferred form, the anchoring points in the central and front zones are separated longitudinally by a distance of between 200 and 230 millimeters.
Moreover, the positioning of the platform on the ski determines the stiffness distribution. Hence, according to the invention, the central anchoring point is advantageously arranged in front of the boot middle marker drawn on the ski, that is to say between 5 and 50 millimeters forward in the direction of the tip and, advantageously, between 20 and 35 millimeters.
Advantageously, in practice, the ski may comprise a second block of elastic material, which comes into contact with the rear end of the platform and is also compressible during the relative movements of the platform in relation to the upper face of the board.
In a preferred form, the platform may comprise a rear anchoring point, that is to say one situated close to the rear foot, and this anchoring point may be designed to connect the rear of the platform to the ski with sliding or, advantageously, without sliding. The latter case involves keeping the rear of the platform bearing on the top of the ski and keeping the lateral guidance, but allowing the ski to displace longitudinally at this anchoring point.
Advantageously, in practice, the block or blocks may have a hardness of between 40 Shore A and 95 Shore A.
In a particular form, the hardness of the front block may be greater than that of the rear block, and this makes it possible to stiffen the front of the ski, which is beneficial because it is the front of the ski that, by carving firmly in the snow, permits good control when turning (without side slipping or juddering).